Proposal: introduce a new class visibility keyword analogous to the recent "file", but with "directory"-level scope

[FrancescoBonizzi]

The current file modifier limits class visibility to a single file. However, many projects are organized by directory, and it is often desirable to encapsulate helper types or dto types within a directory rather than exposing them assembly-wide (internal) or restricting to a single file.

Introducing a directory keyword would enable developers to define types visible only to code within the same directory, improving encapsulation and code organization in large codebases.

For example:

/Repositories
    /User
        UserRepository.cs
        UserDto.cs -> directory visibility only
        UserFilterDto.cs -> directory visibility only

A class declared with the directory modifier is accessible to other code files in the same physical directory, but not outside it. This would provide a visibility granularity between file and internal.

What do you think about it?

[jaredpar]

Have you seen this proposal to add namespace and private modifiers? That is similar in intent to what you're proposing here. Essentially more knobs for isolating code based on the existing structure.

For this specifically, I'm pretty skeptical about introducing the idea of C# language semantics being tied to physical file structures. I think it would be better to lean into other mechanisms for new code isolation knobs.

[FrancescoBonizzi]

Thanks a lot. It seems a very interesting solution and it solves my issues!